No overflow protection for `i32 as usize` in this crate

[namse]

I found that some codes change i32 to usize without any overflow protection, like

psd/src/sections/layer_and_mask_information_section/layer.rs

Line 436 in 5276ab7

let top_in_psd = idx / self.width() as usize + self.layer_properties.layer_top as usize;

I am facing the overflow error on my product.